1. Field of the Invention
This invention relates to safety belts, and more particularly, to passive restraint safety belts in a vehicle using a variable torque direct current motor for transferring the belt between the restraint and release configurations.
2. Description of the Prior Art
Passive safety belt systems generally have one or more retractors connected to the belt to adjust the length of the belt between the release and the restraint positions. In the restraint position, the belt must be variably withdrawn from or retracted in the retractors so as to accommodate comfortably the passenger's seating position. Further, in an emergency situation, the belt must not be able to be withdrawn so as to restrain the passenger.
In most retractors, a spring drives a belt reel to rewind the belt and augments the power of the belt transfer drive in moving the belt to the restraint configuration. When the belt is unwound, some power is required to load the spring. Therefore, in a belt system in which a D.C. motor is used to drive the transfer belt between the release and restraint positions, the belt transfer time from the restraint position to the release position takes longer than the opposite direction because of the different power outputs required in forward and reverse.
The time difference is often disconcerting to the vehicle passengers. The elimination of this time difference is, of course, desirable. The prior art includes two ways of dealing with this time difference. In one method, a resistance is inserted in series with the D.C. motor circuit during the transfer from release to restraint to decrease the torque of the motor to equalize the transfer time duration. In the second method, an auxiliary spring is inserted into the output shaft section of the D.C. motor and stores energy during the time of transfer from release to restraint. The accumulated energy is added to the motor output when the belt is transferred from the restraint to the release position. This provides equalization of the transfer times. In the resistance type, a great amount of heat is generated by the resistance element during the transfer time from release to restraint, thereby restricting the choice of mounting places for the resistance element. The resistance requires space, is somewhat complicated, and the power loss from the resistance shortens the life of the vehicle battery.
The auxiliary spring is generally located along with the motor inside the vehicle door. However, the space within the door is often too small to accommodate it. Moreover, the spring often has poor reliability, and fails before 100 thousand repetitions. It is also difficult to determine the proper number of turns in the spring. The above and other problems are important disadvantages that diminish the practical commercial value of known devices.
The present invention overcomes these and other problems by a variable torque D.C. motor that produces different torques in the two transfer modes (forward and reverse) to equalize the transfer times.